The increasing capacity of digital systems to model, emulate, process or synthesize rich, complex behaviors has engendered a corresponding need for control devices to mediate the dynamics of the behavior; the more complex the dynamics, the more numerous will be the degrees of freedom subject to control and, consequently, the less suited the system will be traditional computer control devices (such as a mouse or joystick). Unless the human user's physical "degrees of freedom" can be efficiently used to exert multidimensional control over the complex system degrees of freedom, effective and natural control will not be possible.
In a sense, this is the essence of musical conducting. Each musical instrument in an orchestra is a unique, complex system in its own right, having many degrees of freedom and capable of different behaviors depending on the style and skill of the musician. Orchestral performance of many instruments multiplies the dynamic possibilities dramatically. Conducting, which has been defined as "leading and coordinating a group of singers and/or instrumentalists in a musical performance or rehearsal" (Randel, The New Harvard Dictionary of Music), represents the use of a full range of human gesture to manipulate a highly complex system. The range of control afforded a conductor through gesture is vast compared with, for example, that obtainable with a mouse or a joystick, which are restricted to movement in two dimensions.
Efforts have been made to automate the process of conducting--or stated more broadly, to utilize gestural input for human-computer interaction--for many years. During the 1960s, for example, Mathews and Rosler developed a light-pen interface, which allowed users to trace their musical intentions on a screen and see its graphical result before actually processing it into a musical output. More recently, Mathews created a device called the "Radio Baton," which uses a coordinate system of radio receivers to determine its position. The array of receivers sends position values to a control computer, which, in turn, sends performance commands to a music computer (see http://ccrma-www.stanford.edu/CCRMA/Overview/).
A wand-shaped, wireless remote sensing device disclosed in 1983, designed as an input device for conducting, made use of ultrasonic (sonar) techniques to locate its position in space. The device was held so as to reflect ultrasonic signals back to a Polaroid ultrasonic rangefinder, which sensed the motion and modeled an image of the baton, and transmitted this information to a computer for analysis.
A complex "two-handed" conducting system, disclosed in 1991, utilized a camera viewer and charge-coupled device (i.e., a "CCD" video camera) to track right-handed motions of a baton and a "data glove" to sense left-hand gestures by measuring the position-coordinates of the fingers. See Morita et al., "A Computer Music System that Follows a Human Conductor," Computer Magazine (July 1991) at 44-53.
A system designed to measure gestural forces rather than positions or trajectories of feature points (as was done by Morita et al.) utilized a three-dimensional accelerometer (an inertial sensor that detects changes along three orthogonal coordinate axes). A software system extracted "kinetic parameters" and interpreted gestures. See Sawada et al., "Gesture Analysis Using 3D Acceleration for Music Control," Proc. Int'l. Comp. Music Conf. (1995) at 257-60.
Another accelerometer-based system consisted of a brass tube containing a simple handmade accelerometer, connected to a belt-pack unit with an AM transmitter and two switches (`stop/continue` and `reset`). The belt-pack transmitted three channels of information (data from the acclerometer and switches) to an AM receiver. A microprocessor decoded this information, translated it into a MIDI-like code, and sent that code to command-sequencing software on a computer. See Keane et al., "The MIDI Baton II," Proc. Int'l. Comp. Music Conf. (1990) (supplemental pages).
All of these systems represent somewhat cumbersome efforts capable of modeling only a few of the most relevant gestural parameters available to a conductor. They burden the user with obstructive, distracting devices and accoutrements unfamiliar to conductors, while failing to provide him or her with the conductor's most familiar instrument--a baton that may be held and manipulated in the traditional fashion without encumbrance or fatigue.